The present invention relates to photocurable coating formulations and, more particularly, the invention relates to a precursor material that can be converted in situ after polymerization to a U.V. absorber.
Photocuring is convenient, rapid and easily automated. It is the method of choice in applications where uniformity of the coating is critical. The development of solar thermal technology is mainly limited by the cost of high performance polymeric reflectors and enclosures for heliostats. Photocuring or photopolymerization constitutes an attractive, low cost energy-conserving process which combines the operations of generation of the polymer and forming the polymer into components.
Photocuring consumes little energy since it is a low temperature, ambient process. It also produces a superior quality, very high molecular weight polymer since thermally activated branching mechanisms are reduced to a minimum. Laminates can be built up with successively applied photocured layers. This obviates the need for adhesive or primer layers. Thin layers are formed in seconds or fractions of a second. There are a wide variety of photocurable vinyl monomers, particularly acrylics, with a wide variety of properties that can be combined by means of copolymers or laminates. For example, the excellent weatherability of acrylics can be combined with the fracture toughness of certain acrylates. Indeed, acrylics could be combined with intermediate layers of cross-linked elastomers for maximizing tear strength while retaining surface hardness, gloss and soil resistance. Certain fluoracrylates are known to be hard, antisoiling and antireflective. They have higher specular transmission than a commonly used fluoropolymer for solar thermal applications, because fluoroacrylates can be completely amorphous and have no scattering centers.
However, many of the substrates coated with the curable coatings and sometimes the coatings themselves are sensitive to ultraviolet radiation and will degrade unless the coating contains ultraviolet absorbers. Currently available photocuring technology has a major limitation since the U.V. absorbers which are incorporated into the coating to protect the substrate or to stabilize the coating compete for the incident actinic radiation, thus inhibiting the photocuring process which can increase the energy demand of the curing source or provide too slow a curing rate and/or incomplete cure.